The present invention relates to apparatus and methods for repairing damaged tenons on the tips of turbine buckets and particularly relates to apparatus and methods for repairing eroded tenons with reduced manufacturing cycle time, costs, labor and improved quality.
Turbine buckets, for example, steam turbine buckets, are typically provided with an annular cover overlying the tips of the buckets. The covers are used to dampen and stiffen the response of the buckets and also provide a circular band on which a seal can be provided. The covers are conventionally provided in arcuate segments overlying a plurality of bucket tips. In the originally manufactured bucket, one or more tenons are provided projecting from the tip of the bucket and are received in corresponding openings in the cover. The tenons are then peened or otherwise secured to the covers to retain the covers on the buckets. Over time and extended usage of the turbine, particularly steam turbines, the bucket tenons corrode away, requiring the bucket/cover assembly to be refurbished by repairing the tenons and resecuring the cover to the bucket tips.
Previously, to repair bucket tenons, the buckets were removed from the turbine with each individual bucket being placed on a workbench. The corroded tenon was then ground away down to a nub on the tip or flush with the bucket tip. The tenon tip was preheated and cleaned. Weld material was then applied to the tip manually in multiple passes, paying strict attention to the magnitude of the preheat. The weld buildup was then stress-relieved and machined to form the new or repaired tenons. This prior process was manually performed, tedious and costly, resulting in very low production rates.